Process for concentration of solutions by sublimation



Nov. 19, 1957 c. BERGER 2,813,350

PROCESS FOR CONCENTRATION OF SOLUTIONS BY SUBLTMATION Filed March l2, 1954 2 Sheets-Sheet 1 fag: z,

4/1 Q l` INVENTOR.

C. BERGER Nov. 19, 1957 PROCESS FOR CONCENTRATION OF SOLUTIONS BY SUBLIMATION l 2 Shees-Sheet 2 Filed March l2, 1954 INVENTOR.

CARL BERGER ,BY 65%@ ATTORNEYS PROCESS FOR CONCENTRATION -2 Claims. (Cl. 34h-5p oF ,soLUTroNS This invention `relates `.to -a `.method `and apparatus for effecting the concentration of solutions.

.Laboratory :methods which rely upon sublimation f'techniques for effecting .solute concentration are .slow and laborious ,and hthe `apparatus utilized `therefor is without f/eifectiue Vmeans forcycliug kof solution .during concentration. .Itis :accordingly afprimary object of this invention to ,provide -a -method for concentrating solutions which Lrn-ethod is rapid, .not deleterious -to Fthe product, .not `limited by eutectic factors, and -is vuseful vfor comtmercial lproduction .purposes ,y .It isyet `another object of the Linvention to provide -a movel apparatus varrangement 4for `Ieiect-ing concentration ,of solutions :by a -combination of `sublimation yand evaporation methods.

g .and other allied objects of 4the invention `are jachieved,.:generally speaking, `by, spray-ing the solution vvhichis to -be `concentraredinto a ,fine-mist tor-m, (freezing the Jmiento ,produce .small solid ,particles of `large surface area,- and v.rerum/fing-,frorn thevicinity of the surface of pantliclesgthe vapors -of solvent. y p

.ln the gprefer-red .practice of `the :invention Ythe `solution is "initially cooled to 'a temperature slightly .above the freezing Ipoint thereof, `sprayed into evacuated `zone frozen .into acontinuously.movingfstream, thezsolvent vapors. `being .collected `as the `stream ,passes =on Ato =a United dtates Patent collection `gpoint lfor `the particles. Vacuum `conditions i-n V this preferred method are maintained while withdrawing the solvent vapors and this `contributes to further evapora-` tion of the solvent. f

The collected solid material .will tbe .readily melted and -it may be recycled 'for further concentration in the same The solvent -is itself easily l'collectible fior 4further use which is -alparticularlyirriportant feature in fooninaction 'with lthe ,more expensive solv'eiits, such 'as alcohol, ill'liftbrleii",`- t#4 l i i i Js'ttluctell and arranged that the -streafm ilne sptayelffmaterial freezes quickly and the temperature of the freezing zone is maintained sufficiently low so that the heat of fusion of the particles is readily removed. Most simply the particles are frozen as they pass through a, vertical tubular chamber having cooling coils in the walls thereof.

The iineness of the particles which occasions a very slow settling thereof through a vertically arranged tube and the provision of vacuum conditions within the equipment plus the relatively large surface area of the particles contributes to the rapid formation of a vapor phase of the solvent and hence contributes also to the concentration of the solids in the particles.

The particles, freed of at least a portion of the solvent in one pass through the apparatus, are collectible in a iluiy mass form and easily remelted for recycling and a second pass through the apparatus to effect substantially any concentration desired.

The invention will be more fully understod by reference to the following detailed description and the drawings wherein:

Figure 1 illustrates apparatus useful in one embodiment 'of fthe invention; 'and :Figure 2 illustrates apparatus useful 1in a `:preferred eem- -bodirnent ofthe invention.

Referring to the 4drawings rthere is .shown at l1 a :closed "tank containing ra solution 3., rfor example, :a il() percent sucrose solution, which is to `.be concentrated. Tire lower lend of the `tank supplied `with a nozzle 5 th'aving very :tine apertures through lwhich fthe liquid man7 be :passe-d to achieve a fine mist form. conduit `|Jiconnetited 'tothe upper rend `:of :the `:tankis adapted sto :passa gas iunder pressure, :preferably 1:an :inert :gas suc-h as "nitrogen, to thesur- 'face vof ithe liquid 3 to develop :sucient pressure for the tormation i-of fthe :spray :and the rne mist. With some Tliquids :andi n'ks 'the head developed `lby the liquid Y,itself 'will be .sulii'cie'nft to effect fthe mist formation.

Cylinder19f-is Sealed to rank1 iin anai-rtightl-elatiouship therewith and che relatively thick `wailluffthis cylinder contains cooling lceils 11, ahaptedfto pass 1any sunable coolant such as ammonia `or IFreon. "ilihefoiiter wall of the `cyln`ider is insulated at 13 'to permit `close temperature control 'within the chamber -of lthe `'cylinder LUand Etor reasons of economy.

'The cylinder wall is also provided 'with a conduit T5 which at the juncture df the wall andeonduit is-provfid'ed *with `a very 'line mesh screen or iilter paper 17 capable of permitting the passage of Ag'ase's but adapted to fretain Isolid particles'strilcing thereagainst. All-'glass filter papers such as those useful in tiltering smoke from air serve ythis purpose. l

rilhe remote end of Vconduit 15 is connected into a'trap I9 also in the form of at'cylinder having insulation `ma -t'eial 20 `therealvout 'and lfurther having Icooling coils 211 in the wall thereof The dependingpoftibn 23 'of conrduwit 15 is adapted toc'onduct vapors passing throughthe *conduit to the cooling Zone which is maintained at 'avery 'low temperaturein the case of the *sucrose solution under consideration about mi"" "toetfectrapid 'coudensati'on irdf `"the Water vapors and the -maintainin'g of controlled `vacuum conditions in Ithe system.A "Conduit T5 "is itself insulated *at 1'16 "to prevent premature `con- "densation pipe "25 ileads from the upper end of trap '19 'to *vacuum pump 27 provided with exhaust port '28; jpunijp is adapted to be driven "by motor `29 to 'provide rlovv vacuum conditions "in 'the trap and the *chamber of the cylinder 9.

A't "its 'lower-end the "trap T9 is :provi-ded with steam heatingcoils 31 'energizablewhen desirable through conduits 32 to melt solvent "in the 'trap 'and a 'tap '3.3 lis provided to *permit Withdrawal of liqu'id solvent.

lfe'fering 'again 'to cylinder "9 the lower `end 'thereof is provided with a steam heating coil 10 and matter collected at 12 intimately contacts the coil and is melted intermittently upon application of steam to the coil and concentrated material flows through pipe 35 to tank 37 when valve 36 is opened and pump 44 is operated. The cooling coils are preferably inoperative when the heat is applied to the mass.

To occasion the flow of the liquid, particularly under viscous conditions thereof, it is necessary to break the Vvacuum in cylinder 9 and this is accomplished by closing the valve 39 of conduit 15 and opening the valve 41 in the cylinder 9 to admit air or more suitably an inert gas through line 42 to the cylinder itself. Upon closing of valve 41 and reopening valve 39 any gas remaining in the chamber will be drawn through the trap 19, pump 27 to exhaust 28 by operation of the motor 29.

The liquid in tank 37 when sufficiently concentrated is driven off through tap 43; the liquid if desired may be drawn through line 45 by pump 47 and recycled to tank 1 through pipe 49, which latter is provided with valve 50 .to the tank.

.pressure within the chamber.

v` to prevent the passage of gas backwardly through the liney when the same is not in operation. Conduit 7 is provided with a valve 52 which shuts oli the ow of inert gas to the tank 1 when the pump 47 is operating to recycle liquid The sugar solution thus referred to, in the operation of the apparatus, is sprayed into the chamber of cylinder 9 and forms a fine mist, the particles of which are frozen to solid form as they descend slowly through the chamber of the cylinder 9. The sucrose solution mist will, when the chamber 9 is maintained at a temperature of about minus3 to about minus 5 degrees C. be frozen to solid particle form before the particles are midway of the vertical length of the cylinder.

Due to the large surface area of the very small particles and due also to the vacuum conditions within the chamber water Vapor forms rapidly even at the low temperature and is drawn through the conduit to the trap 19. The

' descent of the particles is slow and due to their size and the rate of descent may be controlled by limiting the vapor For the sucrose solution under consideration a pressure of about 2 inches of water .within the chamber will produce satisfactory conditions for concentration by sublimation.

The particles themselves for the most part pass directly down the chamber although a few may, under the influence of the vacuum con-dition, strike the lter and/ or sidewalls; accordingly most of the flowing mass is directly collectible in the lower portion of the chamber and when the same is melted the iilter and the wall itself will be freed of solid particles by melting of the particles.

Concentration of the solution to 50 percent by weight of sugar may be effected in three or four passes of the apparatus and the mass is then drawn olf through tap 33.

In Figure 2 numerals similar to Figure l but primed have been employed to indicate like parts and the cylinder 9 connects the other associated vacuum and circulation apparatus just as does the cylinder 9 of Figure l.

Cylinder 9 as illustrated is relatively long and narrow, suitable dimensions being 35 ft. long by 4 ft. in diameter. Such cylinders are particularly useful where the particles normally tend to settle fairly rapidly.

In the apparatus of Figure 2 the cooling coils 11' extend upwardly to about one-half or a little more of the length of the cylinder and the aim is to have the particles freeze just as they pass the point indicated at E. Upwardly of point E in zone A a slightly normal condition prevails and the particles of the mist lose solvent by evaporation. Heat of fusion evolved at E as the particles freeze tends to rise and maintain zone A in such condition that the evaporation of solvent from the particles will be substantial-Such evolved solvent is then drawn olf through the vacuum line as is sublimed solvent as described in connection with Figure 1.

The apparatus of Figure 2 thus comprises a combination of sublimation and evaporation processes which im- 4 prove the efficiency of the operation particularly under those conditions where the particles tend to settle rapidly.

In Figure 2 the heating coils 14 are electrical and imbedded in the wall of the cylinder 9 and are operated alternatively with the cooling coils 11. In connection with the cooling coils of Figure 2 they, like the cooling coils of Figure l, may employ any suitable coolant medium.

It is further to be noted that the trap such as that shown in Figure l may itself contain any suitable medium which would permit of absorption of the solvent withdrawn from the solution, if such absorption is desired, for example, sulfuric acid or phosphorous pentaoxide may be employed.

It will be understood that this invention is susceptible to modification in order to adopt it to different usages and conditions and accordingly, it is desired to comprehend such modifications within this invention as may fall within the scope of the appended claims.

I claim:

1. A process for concentrating solutions comprising the steps of initially cooling the solution to be concentrated to a temperature near the freezing point of the solution, evacuating a closed zone, spraying said solution into said zone in the form of a freely falling mist, freezing the mist particles as the same move downwardly through the evacuated zone to bring about sublimation and evaporation of the solvent therefrom, maintaining the evacuated condition while withdrawing solvent vapors vthus produced, collecting the residual particles and melting the same to a liquid back through the said evacuated closed Zone, and thereafter recycling said liquid and recovering a concentrate.

2. A process for concentrating solutions comprising the steps of initially cooling the solution to be concentrated to a temperature near the freezing point of the solution, evacuating a closed zone, spraying said solution into said zone in the form of a freely falling mist, freezing the mist particles as the same are retained in the evacuated zone to bring about sublimation and evaporation of the solvent therefrom, withdrawing said solvent vapors and condensing the same to recover the solvent, collecting the residual particles, heating the same to form a -uid mass, and recycling said mass back through the said evacuated closed zone and recovering a concentrate.

References Cited in the le of this patent UNITED STATES PATENTS 996,832 Campbell July 4, 1911 2,100,151 Tietz Nov. 23, 1937 2,301,595 Washburn Nov. 10, 1942 2,400,748 Flosdorf May 21, 1946 2,471,035 Hurd May 24, 1949 2,616,604 Folsom Nov. 4, 1952 

